1. [Technical Field]
The present invention relates to a protection circuit module for a secondary battery and a battery package using the same.
2. [Background Art]
Secondary batteries, which can be charged and discharged repeatedly, are often used as batteries to be mounted in a variety of portable information apparatuses. Prevention of degradation of, supplying power for a long period of time to, downsizing of, and inexpensiveness of secondary batteries are considered important. Conventionally, for instance, battery packages of a lithium ion battery have a built-in protection circuit module in which is mounted a protection circuit for preventing the battery from being degraded by excessive heat generation due to an overcurrent caused to flow by short-circuiting of an electric circuit or incorrect charging (a large voltage or reverse voltage).
For instance, there is a protection circuit that has a transistor for current control formed of a MOS transistor interposed in series in the charging and discharging circuit of a secondary battery, that is, between the secondary battery and an external connection terminal to which a charger or a load is connected, so as to be configured to stop charging by setting a current control transistor for charging control in the OFF state at the time of abnormal charging and stop discharging by setting a current control transistor for discharging control in the OFF state at the time of abnormal discharging (see Patent Document 1).
FIG. 10 shows a circuit diagram of a protection circuit module of a secondary battery.
In the protection circuit, a secondary battery 48 is connected between battery-side external terminals 44a and 44b, an external apparatus 50 is connected between load-side external terminals 46a and 46b, the battery-side external terminal 44a and the load-side external terminal 46a are connected by a plus-side charging and discharging circuit 52a, and the battery-side external terminal 44b and the load-side external terminal 46b are connected by a minus-side charging and discharging circuit 52b. A current control transistor 54 and a current control transistor 56 are connected in series to the charging and discharging circuit 52b. The current control transistors 54 and 56 are formed of field effect transistors.
A protection IC (Integrated circuit) chip 58 is connected between the charging and discharging circuits 52a and 52b. A supply voltage terminal 58a of the protection IC chip 58 is connected to the charging and discharging circuit 52a through a resistive element 60, a ground terminal 58b of the protection IC chip 58 is connected to the charging and discharging circuit 52b between the battery-side external terminal 44b and the current control transistor 54, and a charger minus potential input terminal 58c is connected through a resistive element 62 to the charging and discharging circuit 52b between the load-side external terminal 46b and the current control transistor 56. A capacitor 64 is connected between the supply voltage terminal 58a and the ground terminal 58b. An over-discharge detection output terminal 58d is connected to the gate of the current control transistor 54. An overcharge detection output terminal 58e is connected to the gate of the current control transistor 56.
A PTC element 66 is connected between the battery-side external terminal 44b and the secondary battery 48.
In the conventional protection circuit module having such a protection circuit, a package product is employed as the current control transistors 54 and 56 and the protection IC chip 58, which are semiconductor components, and the package product is mounted on a wiring board.
However, it has been a problem that the package product, in which semiconductor chips and lead terminals are connected with bonding wires, causes an increase in cost. Further, it has been a problem that in the current control transistors 54 and 56, in which semiconductor chips are electrically connected to the wiring board through bonding wires and lead terminals, it is impossible to reduce ON resistance.
In order to solve these problems, there is one using COB (Chip On Board), which mounts a bare chip on a wiring board and connects chip electrodes and the wiring board through bonding wires (see, for instance, Patent Document 2 and Patent Document 3).
However, gold, which is costly, is used as the material of the bonding wires. Accordingly, it has been a problem that there is a limit to cost reduction. Further, it has been a problem that in current control transistors, in which semiconductor chips are electrically connected to the wiring board through bonding wires, it is impossible to reduce ON resistance.
Further, there is a mounting method that mounts a bare chip having multiple external connection terminals arranged on a single plane on a wiring board in a face-down manner (also referred to as flip-chip bonding) (see, for instance, Patent Document 4). Further, there is a protection circuit module for a secondary battery that has a protection IC chip and current control transistors, which are semiconductor components, mounted face-down on a wiring board (see, for instance, Patent Document 5).
Mounting semiconductor components on a wiring board in a face-down manner makes it possible to reduce cost and decrease an area for mounting the semiconductor components compared with the case of using a wiring bonding technique. Further, it is also possible to reduce the ON resistance of field effect transistors.
[Patent Document 1] Japanese Laid-Open Patent Application No. 2001-61232
[Patent Document 2] Japanese Laid-Open Patent Application No. 2002-141506 (Page 2, Page 4, FIG. 2 and FIG. 3)
[Patent Document 3] Japanese Laid-Open Patent Application No. 2002-314029 (Pages 2-3, FIG. 14 and FIG. 15)
[Patent Document 4] Japanese Laid-Open Patent Application No. 10-112481
[Patent Document 5] Japanese Laid-Open Patent Application No. 2000-307052
[Patent Document 6] Japanese Laid-Open Patent Application No. 2003-31595
In a conventional protection circuit module for a secondary battery, battery-side external terminals to be connected to the secondary battery and load-side external terminals to be connected to a load occupy a large area. Further, it is also required to reduce the protection circuit module in size in response to a request for downsizing of a battery package.